Influence of the shape of the pacing pulse on ventricular excitation threshold and the function of skeletal muscles in the operating field during non-invasive transcutaneous cardiac pacing under general anaesthesia.

BACKGROUND Transcutaneous cardiac pacing (TCP) in patients under general anesthesia does not pose a problem of pain threshold for high amplitudes of pacing pulses, but their application causes contractions of skeletal muscles, which is a problem during surgery. Evaluation of the influence of various shapes of the pacing pulse on the ventricular excitation threshold, the electric energy transmitted to the system of electrodes and the movement of the operating field during TCP performed under general anesthesia. METHODS The study included 58 patients operated under general anesthesia with TCP performed subsequently by means of rectangular pulses, square of the sinus and root of the sinus shaped pulses with identical pulse base width of 40 ms. RESULTS With incomplete muscle relaxation, for the amplitudes of up to 120 mA, the pacing was the most efficient (94%), ventricular excitation thresholds (VET) were the lowest, i.e. 70.5 +/- 18.3 mA on average, and the operating field was the most stable when rectangular pulse was applied. The lowest electrical energy, i.e. 44.0 +/- 13.8 mJ on average, was provided to the system of electrodes by the pulse shaped like the square of the sinus. The rectangular pulse caused the earliest excitation of skeletal muscles at 40.5 +/- 15.6 mA on the average. However, in the conditions of complete muscle relaxation, the skeletal muscle excitation thresholds doubled, which greatly reduced the movement of the operating field. CONCLUSIONS The rectangular pacing pulse ensured the lowest VET, the least movement of the operating field and the most efficient pacing during TCP under general anesthesia. The square of the sinus shaped pulse allowed for the lowest electrical energy applied to the heart. Owing to full skeletal muscle relaxation, the surgeon operated in a stable operating field. (Cardiol J 2007; 14: 137-142).